Occlusion of coronary arteries can proceed to the point where a myocardial infarction, that is a heart attack, occurs. Various procedures and therapies are used to reduce or eliminate blockages within the coronary vessels. One method used to treat vascular vessels is angioplasty, in which an expansible element, typically a balloon, is passed through the vessel to the target site and expanded to dilate the vessel and thus restore adequate blood flow through the vessel. One of the problems with angioplasty is that it is subject to restenosis, that is the renarrowing of the vessel after the vessel has been widened by the angioplasty procedure. Various ways have been used to help prevent this restenosis, including athrectomy, stenting, laser techniques, and the use of various pharmacological compositions including calcium antagonists, ace inhibitors, fish oils and steroids.
Another approach used to help prevent restenosis is through irradiation of the target site. This approach is described in, for example, U.S. Patent Nos. 5,484,384 and 5,840,008. One of the keys to radiation therapy is the controlled, typically uniform, irradiation of the target tissue. It is undesirable to provide too much or too little radiation to all or parts of the target site. Other problems associated with irradiating vessels include shielding the radiation source when not being used to actively irradiate the target site, and ensuring the safety of the medical personnel before, during and after the radiation procedure.
The present invention is directed to a medical irradiation assembly and method which ensures that the target site within a vessel is provided with a uniform, controlled dose of radiation in a simple, safe and effective manner.
A first aspect of the invention is directed to a catheter having an expansible membrane near its distal end and a continuous loop, circumferentially-extending radiation source configured to be expansible within the expansible membrane and to be axially translated along and in contact with the inner surface of the expansible membrane. The expansible membrane is typically a balloon. The radiation source may be mounted to an elongate manipulator. The expansible radiation source may be self-expanding or may be selectively expansible. The expansible radiation source may be, for example, a single radioactive loop.
Another aspect of the invention is directed to a medical irradiation assembly including a balloon catheter having an inflatable balloon with an inside surface, a continuous loop, circumferentially-extending radiation source placeable along a circumferential path against the inside surface of the balloon when the balloon is inflated, and a manipulator for moving the radiation source through the balloon while maintaining contact with the balloon. One or more radiation shields may be used to house the radiation source, preferably a xcex2 source, when not in use.
A further aspect of the invention is directed to a method for delivering a radiation dose to a body lumen by expanding a membrane against a wall of the body lumen and passing a continuous loop, circumferentially-extending radiation source along and in contact with the inner surface of the membrane so that radiation passes into the wall of the lumen. The radiation source may be shielded before and after it is passed along the inner surface of the membrane.
A still further aspect of the invention is directed to a kit including an expansible membrane, an irradiation source and instructions for use as discussed above.
With the present invention the continuous-loop radiation source can be made to stay in contact with the membrane. This ensures (1) that the radiation source remains a constant distance, the thickness of the membrane in a preferred embodiment, from the target tissue, and (2) that there are no gaps as exist between conventional discrete, spaced-apart radiation sources; as a result, the target tissue can be irradiated uniformly. This is important when the effectiveness of the irradiation is very sensitive to distance from the target tissue, as it is with many xcex2 radiation sources.
Another advantage of the present invention is that it enables the effective shielding of the radiation source before and after the actual procedure. Also, effective shielding is aided by using a xcex2 source as the radiation source.
Other features and advantages of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawings.